CVE-2023-48230Network attack vector

Remote service crash via WebSocket compression mismatch

Published Nov 21, 2023 · Updated Aug 2, 2024

Buffer underwrite in the KJ HTTP WebSocket parser in Cap'n Proto 1.0 through 1.0.1 allows remote attackers to crash services. The parser allocates only the payload length when a negotiated-compression frame lacks the compression bit, then writes a four-byte zlib trailer before the heap buffer. WebSocket compression must be enabled; the constant overwrite corrupts allocator state and causes a later allocation to crash.

CVSS severity5.9
Medium
EPSS probability1.89%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Buffer underwrite in the KJ HTTP WebSocket parser in Cap'n Proto 1.0 through 1.0.1 allows remote attackers to crash services. The parser allocates only the payload length when a negotiated-compression frame lacks the compression bit, then writes a four-byte zlib trailer before the heap buffer. WebSocket compression must be enabled; the constant overwrite corrupts allocator state and causes a later allocation to crash.

The record

CVE
CVE-2023-48230
Published
Nov 21, 2023
Updated
Aug 2, 2024
Vendor
Cap'n Proto
Product
Cap'n Proto
Classifications
CWE-124, T1499.004
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Nov 21, 2023CVE publishedPublication date reported by the CVE source.
  2. Aug 2, 2024Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=>= 1.0, < 1.0.1.1

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Cap'n Proto · Cap'n Protoversion=>= 1.0, < 1.0.1.1

Published CVSS scores

5.9GitHub, Inc.CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H
9.8NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-124Buffer Underwrite ('Buffer Underflow')
T1499.004Application or System Exploitation

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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